Sam Kleemann 1, Rick Llewellyn 2, Bill Davoren 2, Gurjeet Gill 1, Chris Preston 1, Therese McBeath 2
1 University of Adelaide and 2 CSIRO Agriculture
Peer review: Andrew Smith, CSIRO
Brome grass is the most costly weed to grain production in the Mallee region despite herbicide resistance being relatively low. For growers looking to reduce reliance on Group B herbicides, pre-emergence herbicides can be an important part of brome management strategies but trifluralin has limited efficacy. Previous pre-emergence herbicide trials at the MSF Karoonda site have shown the potential for greater than 75% brome control, but also the potential for variability under different early-season conditions.
Why was the project done?
The treatments applied on a non-wetting sand at the MSF Karoonda site were aimed at testing whether extra investment in alternative pre-emergent herbicide treatments can lead to better brome control under different no-till seeding conditions. The trial used Kord wheat and compared: 1. Trifluralin (control) at standard local rate (1.5 L/ha); 2. Trifluralin + Metribuzin (1.5 L/ha + 150 g/ha); 3. Trifluralin + Metribuzin + post emergence Avadex Xtra (1.5 L/ha + 150 g/ha + 2.0 L/ha); 4. Trifluralin + Avadex Xtra (1.5 L/ha + 2.0 L/ha); 5. Sakura (118 g/ha); 6. Sakura + Avadex Xtra (118 g/ha + 3.2 L/ha); 7. Sakura + Metribuzin (118 g/ha + 150 g/ha). The herbicides were tested under marginal soil moisture conditions at seeding that resulted in poor crop emergence (30 April seeding: 49 crop plants/m2; 20 May seeding: 21 crop plants/m2) that led to patchy competition from the crop.
• The later seeding had very poor crop establishment, resulting in significantly higher brome seed production (115% more panicles) than early seeding, but seeding time did not interact with herbicide treatment effects.
• Only the treatments including Sakura resulted in significantly (P<0.01) better brome control than trifluralin alone (measured by number of panicles/m2).
• Sakura alone resulted in 55% less brome panicles than trifluralin alone, and Sakura + Avadex resulted in 72% less brome panicles than trifluralin alone.
• Sakura’s extended residual soil activity, which can restrict root growth of brome, combined with the dry spring, was probably responsible for the reduced seed set.
• Substantially better brome control and seedset reduction is possible by using pre-emergence options other than trifluralin. The additional herbicide cost needs to be evaluated against the better level of control, including the longer-term seedbank benefits.